On an immunochromatographic test strip, an antibody (or antigen) that causes an antigen-antibody reaction with an antigen (or antibody) in a sample is coated in advance in a band-like manner in a reaction region. When a dye-labeled antigen (or antibody) in the sample is developed to the reaction region of the test strip, the antigen (or antibody) in the sample causes the antigen-antibody reaction with the antibody (or antigen) coated in band-like manner and becomes trapped, and a line colored by the dye is formed in the reaction region. With such an immunochromatographic test strip, by using a measuring apparatus to optically measure a coloration degree (reaction degree) of the line formed in the reaction region, an amount of the antigen (or antibody) in the sample can be analyzed quantitatively.
Each of Patent Documents 1 to 3 discloses an apparatus that illuminates light on an immunochromatographic test strip and detects an intensity of reflected light to measure the coloration degree of the test strip. In the apparatus disclosed in Patent Document 1, the test strip is moved with respect to a measuring system (a light emitting unit and a light receiving unit) that is fixed in position and the reflected light is detected in a continuous manner to measure the coloration degree. The apparatus disclosed in Patent Document 2 has a plurality of light emitting elements and light receiving elements disposed in parallel along a direction in which the sample flows (develops) and measures the coloration degree based on the intensity of the light reflected to the respective light receiving elements. With the apparatus described in Patent Document 3, a change of reflected light intensity is sensed at an arbitrary point on the test strip and measurement is started automatically after a fixed time from the change.    Patent Document 1: Japanese Published Unexamined Patent Application No. Hei 11-83745    Patent Document 2: Japanese Published Unexamined Patent Application No. Hei 10-274624    Patent Document 3: Japanese Published Unexamined Patent Application No. 2003-4743